The deposition of cathodoluminescent materials onto cathode ray tube (CRT) substrates requires a method which accurately positions the particles and which causes the particles to firmly adhere to the substrate. This is especially critical for the deposition of phosphors onto substrates such as faceplates used in vacuum fluorescent displays (VFDs). The technology now being developed for such flat plate VFDs includes the use of field emitter arrays positioned at very short distances (for example 75 microns) from the cathodoluminescent phosphors as discussed in the article Field Emitter Arrays Applied to Vacuum Fluorescent Displays found at IEEE Transactions on Electron Devices, Vol. 36, No. 1, January 1989. As mentioned there, cathodoluminescence is useful in such applications because much is known about phosphors which are used in CRTs.
Many different methods are known for depositing phosphors on CRT faceplates. For example, in U.S. Pat. No. 3,475,169, phosphors are deposited by development of an exposed photoconductive layer wherein a liquid developer, which includes a polymeric binder, is used. This document discloses both the use of direct and reversal imaging onto a charged photoconductive layer, and mentions the problems of adapting electrostatic printing processes for use in the manufacture of CRTs. While the use of binders is helpful, such binders must be able to survive relatively high temperature bake out steps (about 400.degree. C.) without degradation or discoloration. It has been found that few binders can withstand such temperatures.
U.S. Pat. No. 2,682,478 discloses a method of depositing powdered phosphors on a non-planar television screen (e.g. one having projecting multi-faceted shapes) which includes deposition of charged phosphor particles to an oppositely charged substrate surface. Glass binders may be included in the phosphor powder. Thus, while improved adherence would be expected, this method provides little guidance as to how to accurately define the appropriate deposition areas for a planar substrate.
U.S. Pat. No. 2,959,483 discloses the use of a photosensitive resist layer which is exposed, developed and treated with phosphor and filter materials. Once the phosphor and filter materials have been applied to the surface of the patterned photoresist, the faceplate is heated to remove the resist and fuse these materials to the faceplate. Where phosphors are applied on the surface of the photoresist, however, adherence of the phosphors after the fusing step is found to be unsatisfactory.
Phosphor containing cathodoluminescent materials have also been deposited by applying thin films to a substrate using vacuum evaporation. The difficulty with this approach is that the material to be deposited must be heat treated to about 900.degree. C. to activate it to maximum efficiency. This temperature is not compatible with glasses which are commonly used as a substrate, such glasses having softening points of less than 900.degree. C.